The invention relates to the field of electronic photography, and in particular to an electronic photographic system for capturing images, which are resident on image bearing media, and inputting the captured images to a computer. More specifically, the invention pertains to correction of optical alignment error in a system where an electronic camera is not integral with the image handling device.
A typical approach for capturing images and inputting the captured images to a computer involves an electronic still camera designed to be directly tethered to the computer. For example, U.S. Pat. No. 5,402,170 describes a low cost electronic still camera tethered to a personal computer which provides image processing, storage, and display of the captured images. By relying on the computer to perform these tasks, the camera cost can be greatly reduced. Another example is the Kodak DVC 300 Digital Video Camera, which is attached by cable to a personal computer. The capture of images from image-bearing media, such as film, has usually involved stand-alone scanners. Such devices are expensive and complex, and are also usually dedicated to a single purpose, thus representing a high cost to the average consumer. For example, a color sequential scanner shown in U.S. Pat. No. 5,301,244 uses a computer to perform certain functions, such as color correction, but nonetheless represents a complex, specialized piece of equipment. This high cost for a single purpose device has minimized the utility of conventional photographic film as an image input for desktop computer systems.
In the above-mentioned copending Ser. No. 08/713,057, a relatively simple tethered digital camera is merged with a simple film handling mechanism in order to capture images resident on a film in a simple and inexpensive manner and transmit the captured images to a computer. The film handling mechanism includes a film gate, a housing for supporting the digital camera in a position that images the film gate, a film transport mechanism for transporting the film through the film gate, and an illuminator for illuminating the film gate and the film therewith. By configuring the housing to allow removal of the camera from the film handling mechanism, the user obtains a system which has the utility of normal camera input along with the ability to image film with the same camera. Pursuant to its computer connection, the film handling mechanism includes means responsive to an instruction from the computer for advancing the film frame by frame through the film gate in order to capture the images on the film.
In using a film handling mechanism such as described in copending Ser. No. 08/713,057, optical alignment between the separate components is a special problem. In particular, the difficulty of correctly pointing the camera toward the film gate must be overcome if the image is to be captured successfully. The camera must be adjusted such that the proper lateral pointing is achieved, or the captured image will be off-center. Additionally, if the magnification is not exactly as expected, the captured image may appear too small, or a portion of the image may be cropped. Tolerances necessary to ensure the proper positioning of the camera relative to the image bearing medium are difficult or impossible to achieve. In particular, when a camera is inserted into such a device, there is no guarantee the camera will be positioned such that it will be capturing the desired portion of the image bearing medium.
Generally, the user is forced to make tedious adjustments by trial and error to ensure the camera is capturing the desired portion. Additionally, the mechanisms necessary to make these adjustments increase the cost and complexity of the media handling device. In U.S. Pat. No. 5,278,669, scan data from an original is automatically separated from another portion other than the original without specifying the size of the original. In a prescanning operation, scan data including the original data is produced, Then, an image extracting circuit separates the original region from the other portion by comparing the density of scanned pixel values. This operation, however, is dependent upon the presence of the desired image, and must therefore be repeated for each image scan.
It would be preferable to have an electronic imaging system that can perform field of view correction once for each image capture session, rather than for each image capture.
The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, an imaging system includes an electronic camera having a predetermined field of view for capturing images of image bearing media and a handling mechanism for supporting the image bearing media. The handling mechanism includes a framed region for revealing an image bearing area of the media to the electronic camera and means for supporting the electronic camera in a position that images the framed region while capturing a field of view larger than the image bearing area of the media. A processor associated with the electronic camera provides field of view correction of images captured from the image bearing media by initiating capture of an image of the framed region in the absence of an image bearing area of the media and determining the coordinates of the image bearing area from the image of the framed region. The coordinates of the image bearing area are then used for field of view correction of subsequently captured images. The processor may be located in the electronic camera, or preferably in a host computer attached to the camera. In the latter case, the camera is ordinarily tethered to the computer, which establishes field of view correction for the camera.
The advantage of the invention is that an electronic camera may be used with, e.g., a film handling mechanism without modification to the camera. For the purpose of capturing images on a film, the camera plugs into a nest which positions it to capture the images resident upon the film. The nest contains a film transport mechanism and an illuminator for illuminating the film. By utilizing a low cost digital camera tethered to a computer, the tethered camera captures images from the film in a manner similar to how it is used for office environment capture, and algorithms running on the computer modify the data captured to recreate the actual scene image, particularly from a negative film image. Errors in optical alignment between the camera and the image bearing media are compensated for by initially capturing an area larger than the desired image area. The desired image area is automatically presented to the user by the application, which determines the desired image area from the full captured area.